As I mentioned above I've used prepared by UniPi image of rasbian with evok embedded called "UniPian-Neuron-OS-2018-06-15.img". Reason, why I tried to do upgrade, was that this version didn't work correctly with api commands showed on your documentation, I couldn't control relays. I found in a thread on the forum that was a BUG which was fixed after the image release date.

@wizro_pl The thing is that the evok installed from debian package is not compatible with the one installed as mentioned on github. To make it easier, please use the Raspbian stretch lite and install evok according to the guide on Github. We will publish a UniPian OS with the package version of evok soon.